Experimental Research On NC Bending With Small Bending Radius Of Aluminum Alloy Thin-Walled Tube

Aluminum alloy thin-walled tubes with small bending radius are one of key components widely used in aviation, aerospace high-technology industries. Its NC bending forming is a complicated physical process under coupling interactive effects of multi-factors, and has become one of problems to be urgently resolved in this field. In this paper, the stress and strain distribution, tube wall thinning and the cross section ovalization in Aluminum alloy thin-walled tube NC bending with small bending radius have been investigated through experimental method combined with finite element method and theoretical analysis. A brief introduction to the project and the main achievements are as follows:The formula has been deduced for choosing the maximum mandrel shank extension length considering the effect of mandrel ball. It offers reference for selecting reasonable mandrel shank extension length and designing the mandrel and mandrel ball. General forming defects have been analyzed in thin-walled tube NC bending process and then a simple, effective and credible method for adjusting the dies has been put forward.By using the grid method, the strain distribution laws in Aluminum alloy thin-walled tube NC bending have been obtained. The results show that the tangential strain on the outmost of LF2M tube is larger than that on the innermost. The hoop strain can not be neglected, and the maximal value of the hoop strain even reaches 1/4 of the tangential strain. The shear strain has been neglected on the outmost and innermost of tube, but it is considerable in the others positions.The effects of process parameters on wall thickness thinning and cross section ovalization are studied systematically. The results indicate that with mandrel extension length and mandrel balls number increasing, the wall thinning ratio increases, but the cross section ovalization reduces; Both wall thickness thinning and cross section ovalization become more serious with bending radius or friction coefficient between pressure die and tube decreasing or bending angles increasing; Under the same bending conditions, the wall thickness thinning and cross section ovalization of LF2M tube is larger than that of 1Cr18Ni9Ti tube.